lightningd/plugin: fix read-after-free on plugin options

Thanks sanity checks ! :p

lightningd/plugin.c

@@ -524,8 +524,13 @@ static bool plugin_opt_add(struct plugin *plugin, const char *buffer,
 	if (!defaulttok)
 		popt->description = json_strdup(popt, buffer, desctok);
 	list_add_tail(&plugin->plugin_opts, &popt->list);
-	opt_register_arg(popt->name, plugin_opt_set, NULL, popt,
-				popt->description);
+	/* We duplicate the name, as popt->name will be freed if we
+	 * 'plugin stop' this plugin but it won't be removed from the global
+	 * opt_table ! We could end up reading after free (json_listconfigs).
+	 * FIXME: Cleaner to allow to unregister an option ? */
+	opt_register_arg(tal_strdup(plugin->plugins, popt->name),
+			 plugin_opt_set, NULL, popt,
+			 popt->description);
 	return true;
 }